Understanding the Azure DevOps SQL Task: Column Names in Each Table Must Be Unique

In this article, we will delve into the world of Azure DevOps and explore the SQL task that is causing issues with column names being specified more than once. We’ll discuss the steps to troubleshoot and resolve this issue.

What are Azure DevOps Tasks?

Azure DevOps tasks are components of a pipeline that execute specific actions or scripts in the pipeline environment. In our case, we’re dealing with the SqlAzureDacpacDeployment@1 task, which is used to deploy SQL Dacpac files to an Azure SQL database.

The Problem: Column Names Must Be Unique

The question states that when deploying the first time, the script succeeds without errors, but when deployed the second time, it throws an error. This implies that there’s a mismatch between the column names specified in the script and those already existing in the database.

To better understand this issue, let’s examine the SQL scripts provided:

IF NOT EXISTS (SELECT 1 FROM SYS.COLUMNS WHERE OBJECT_ID = OBJECT_ID(N'[dbo].[test]') AND name = 'currency')
BEGIN
  ALTER TABLE [dbo].[salesorder] ADD currency varchar(10)
END

And

IF NOT EXISTS(SELECT * FROM sys.columns WHERE Name = 'currency' 
              AND object_id = OBJECT_ID('test'))
    BEGIN
        ALTER TABLE test
        ADD currency varchar(10)
    END
ELSE
  BEGIN
    PRINT 'Currency kolom bestaat reeds.'
  END

The first script checks if the currency column exists in table [dbo].[test], and if not, adds it. The second script does a similar check for the salesorder table but uses OBJECT_ID('test') instead of OBJECT_ID(N'[dbo].[test]).

The Issue: Object_ID vs. String Literal

In SQL Server, OBJECT_ID() returns an integer that represents the object ID, which is a unique identifier for each object in the database. When using OBJECT_ID(), you need to pass the name of the object as a string literal.

The problem lies in the fact that Azure DevOps stores objects as integers, not as string literals. When deploying the second time, the OBJECT_ID() function returns different integer values, resulting in the column names being specified more than once.

To fix this issue, we need to ensure that both scripts are using consistent object IDs or string literals.

Solution: Using Object_ID() and Object_Identifer

We can modify the script to use OBJECT_ID() consistently. However, there’s a catch: OBJECT_ID() returns an integer for system objects (like tables) but returns the object identifier of a user-defined object like [dbo].[test].

IF NOT EXISTS (SELECT 1 FROM SYS.COLUMNS WHERE OBJECT_ID = OBJECT_ID(N'[dbo].[test]') AND name = 'currency')
BEGIN
  ALTER TABLE [dbo].[salesorder] ADD currency varchar(10)
END

In the second script, we need to use OBJECT_ID() and cast it to an integer:

IF NOT EXISTS(SELECT * FROM sys.columns WHERE Name = 'currency' 
              AND object_id = CAST(OBJECT_ID('test') AS INT))
    BEGIN
        ALTER TABLE test
        ADD currency varchar(10)
    END
ELSE
  BEGIN
    PRINT 'Currency kolom bestaat reeds.'
  END

Solution: Using Object_Identifer()

Alternatively, we can use OBJECT_IDENTIFIER() function to get the object name as a string:

IF NOT EXISTS(SELECT * FROM sys.columns WHERE Name = 'currency' 
              AND object_id = OBJECT_IDENTIFIER('test'))
    BEGIN
        ALTER TABLE test
        ADD currency varchar(10)
    END
ELSE
  BEGIN
    PRINT 'Currency kolom bestaat reeds.'
  END

Solution: Using String Literal

However, using OBJECT_IDENTIFIER() is not recommended as it may return different values for the same object.

Another solution is to use string literals consistently:

IF NOT EXISTS (SELECT 1 FROM SYS.COLUMNS WHERE OBJECT_ID = OBJECT_ID(N'[dbo].[test]') AND name = 'currency')
BEGIN
  ALTER TABLE [dbo].[salesorder] ADD currency varchar(10)
END

And

IF NOT EXISTS(SELECT * FROM sys.columns WHERE Name = 'currency' 
              AND object_id = OBJECT_ID('test'))
    BEGIN
        ALTER TABLE test
        ADD currency varchar(10)
    END
ELSE
  BEGIN
    PRINT 'Currency kolom bestaat reeds.'
  END

In both cases, we’re using consistent string literals to refer to the test table.

Conclusion

The issue with column names being specified more than once is caused by inconsistent object IDs and string literals. By understanding how Azure DevOps stores objects as integers and using consistent approaches to reference these objects, we can resolve this issue and ensure that our SQL scripts work correctly.

Last modified on 2024-02-07